Lecture-16 - Lecture#16 Today’s Lecture Objectives •...

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Unformatted text preview: Lecture #16 Today’s Lecture Objectives • DNS • HTTP • HTTP DNS Functions • IP and host name address translation – IP address to host – Host to IP address • Host aliasing – Multiple host names per IP address • Mail server aliasing – Specific function for Port 25 – Mail type “MX” • Load distribution – Host to IP address returns multiple IP addresses DNS Misc • Truly distributed – Avoid problems of centralization (which are?) • UDP-based – In most situations – Uses Port 53 • Types of servers – Local: within and serves an admin domain – Root: highest level of DNS “tree” • May point to “Top Level Domain” (TLD) servers (based on suffix, e.g., .com, .edu, .uk, etc.) – Authoritative: the server that maintains a particular DNS record DNS: Root Name Servers • Contacted when local name server cannot resolve name • Root server may then contact authoritative name server if name mapping not known k RIPE London (also Amsterdam, rankfurt) a Verisign, Dulles, VA c Cogent, Herndon, VA (also Los Angeles) d U Maryland College Park, MD g US DoD Vienna, VA 13 root name servers worldwide b USC-ISI Marina del Rey, CA l ICANN Los Angeles, CA e NASA Mt View, CA f Internet Software C. Palo Alto, CA (and 17 other locations) i Autonomica, Stockholm (plus 3 other locations) Frankfurt) m WIDE Tokyo g US DoD Vienna, VA h ARL Aberdeen, MD j Verisign, ( 11 locations) TLD and Authoritative Servers • Root servers – May contact top-level domains for help • Top-level domain (TLD) servers: responsible for com, org, net, edu, etc, and all top-level country domains uk, fr, ca, jp. etwork solutions maintains servers for .com TLD – Network solutions maintains servers for .com TLD – Educause for .edu TLD • Authoritative DNS servers: organization’s DNS servers, providing authoritative hostname to IP mappings for organization’s servers (e.g., Web and mail). – Can be maintained by organization or service provider Local Name Server • Does not strictly belong to hierarchy • Each ISP (residential ISP, company, university) has one. lso called “default name server” – Also called “default name server” • When a host makes a DNS query, query is sent to its local DNS server – Acts as a proxy, forwards query into hierarchy. Two Ways to do Queries • Iterative • Recursive • Can also do a combination of the two in a kind of “hybrid” approach root DNS server 2 3 4 5 TLD DNS server • Host at cis.poly.edu wants IP address for gaia.cs.umass.edu Iterative Queries requesting host cis.poly.edu gaia.cs.umass.edu local DNS server dns.poly.edu 1 6 authoritative DNS server dns.cs.umass.edu 7 8 • Two ways to do queries… root DNS server 2 6 7 TLD DNS server 3 Recursive Queries recursive query: • puts burden of name resolution on contacted server eavy load?...
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This note was uploaded on 02/19/2012 for the course ENGR 361 taught by Professor Drexel during the Spring '12 term at Bloomsburg.

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Lecture-16 - Lecture#16 Today’s Lecture Objectives •...

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